The main objective of this study is to determine the effect of intravenous ABT-431 given in a range of rising, single daily doses (5, 10, 20, and 40 mg) on motor signs and dyskinesia in Parkinson's disease patients with documented levodopa-induced dyskinesia. The effect of ABT-431 will be compared to the effect of intravenous levodopa. A second objective of this study is to assess the safety and pharmacokinetic parameters of ABT-431 in levodopa-treated Parkinson's disease patients.